Activation Energy Analysis of Dark and Laser Illuminated I-V Characteristics of Thin-Film Poly Silicon Solar Cells

Abstract

Abstract The temperature dependence of photocurrent of polycrystalline Si (poly-Si) thin-film solar cells on glass with interdigitated mesa structure has been locally investigated using Infrared Light Beam Induced Current (IR-LBIC) in the temperature range of -25 to +70 °C. The temperature dependence of electrical characteristics of poly-Si thin-film solar cells in reverse bias has been also analysed and compared with the monocrystalline thin-film solar cells. The poly-Si solar cell shows a temperature coefficient (TC) for the photocurrent of around +0.8 and +0.6 %/°C in the grain interior and grain boundary, respectively. The activation energy of the reverse current and also the photocurrent due to the IR laser stimulation has been evaluated, which provide information about traps and their energy levels in the absorber layer of the poly-Si thin-film solar cell. The obtained average value of the activation energy associated with the photocurrent of the poly-Si cell suggests the existence of a shallow acceptor level at around 0.045 eV in the grain boundary and 0.062 eV in the grain interior of the absorber layer of the poly-Si thin-film solar cell. The activation energies of the reverse current for poly-Si and monocrystalline cells have been calculated when the device is biased at -1 and -2 V and the results compared with the activation energy of the saturation current obtained from extrapolation of the I-V curve in the SRH (Shockley-Read-Hall) regime. The results show strong voltage dependence. In both cases the activation energy of the reverse current decreases in the reverse bias voltage, approaching the values obtained from the photocurrent.